Herz
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The influence of Mg2+ and K+ on reoxygenation arrhythmias following 18 min of hypoxia (pO2 about 1 mm Hg, no glucose, 10 mmol/l2-desoxyglucose) has been investigated in isolated guinea-pig left atria (stimulation rate 1 Hz). Duration of reoxygenation arrhythmias was slightly reduced by increase in Mg2+ (0.6 to 4.8 mmol/l) and enhanced by decrease in Mg2+ (0.1 mmol/l), however, this effect was not significantly different from control (0.6 mmol/l). In contrast, low K+ (< 4 mmol/l) led to a significant (p < or = 0.05) prolongation and high K+ (> 5 mmol/l) to a significant abbreviation of reoxygenation arrhythmias. ⋯ Mg2+ (0.6 to 4.8 mmol/l) suppressed late afterdepolarizations and -contractions in K(+)-depolarized guinea-pig papillary muscles (27 mmol/l K+, 0.5 mmol/l Ba2+) induced by 2 x 10(-8) mol/l isoprenaline. The change in the triphasic contraction cycle by elevation of Mg2+ indicates that Mg2+ additionally increases stimulus-induced release of Ca2+ from the sarcoplasmic reticulum and reduces slow Ca2+ inward current. The described electrophysiological actions of the electrolytes represent mechanisms, which may explain their antiarrhythmic actions observed in clinical studies.